Until recently, it has been customary to assign fixed frequencies exclusively to systems and telecommunications providers of each country or region according to their respective needs. However, frequency resources have decreased drastically due to the introduction of high-speed, wide-band radio communication systems and new radio services that have been made possible by wide system frequency bands, advanced radio interfaces, and rapid standardization. Therefore, it is becoming difficult to newly assign fixed frequencies exclusively to newly-introduced radio communication systems.
A technology disclosed in “An alternative concept to scanning process for cognitive radio systems: technical and regulatory issues” (Martigne, P.; Moessner, K.; Cordier, P.; Ben Jemaa, S.; Houze, P.; Agusti, R.; Deschamps, B.; Bender, P.; Jeanty, L.; Bourse, D.; 16th IST Mobile and Wireless Communications Summit, 2007; 1-5 July 2007; pp. 1-5) tries to improve the efficient use of frequency resources by using a cognitive pilot channel (CPC).
FIG. 1 is a drawing illustrating an outline of a system using the CPC. In this system, the entire geographical region covered by the system is divided into areas called meshes and each area (mesh) includes multiple radio systems of the same type or different types. Exemplary radio systems include IMT-2000 systems, Long Term Evolution (LTE) systems, and broadcasting systems for television broadcasting and radio broadcasting. In FIG. 1, it is assumed that two radio systems of telecommunications operators 1 and 2 are providing services in the same area. The CPC includes information on frequencies and radio schemes that is necessary to use radio systems being operated in each area. Therefore, with the CPC, a terminal does not have to scan all available radio systems to connect to a desired radio system. In other words, the terminal can find out and connect to a desired radio system based on information in the CPC. The CPC can also be used to partially change radio system parameters and thereby to construct a flexible radio system as described in “A Novel On-Demand Cognitive Pilot Channel enabling Dynamic Spectrum Allocation, ” J. Perez-Romero, et al., IEEE Dyspan 2007. Thus, using the CPC makes it possible to reduce the prices of terminals, to flexibly change radio system parameters, and to improve the frequency efficiency.